This invention relates to a weighing method and apparatus for obtaining articles of a weight closest to a target weight value. More particularly, the invention relates to a weighing method and apparatus for weighing out batches of articles with great accuracy wherein the articles in a batch have unit weights which differ from one another, such articles being agricultural products such as green peppers and potatoes, lifestock foodstuffs such as meat and broilers, perishable foods, fruits and fabricated parts.
According to a combinatorial weighing method which is known in the art, combinatorial weighing is carried out by weighing articles which have been introduced into a plurality of weighing hoppers, selecting the combination of articles (referred to as the "optimum" combination) which gives a total weight value closest to a target weight value, discharging only the selected articles, subsequently replenishing the emptied weighing hoppers with new articles to prepare for the next combination, and continuing automatic weighing by thenceforth repeating the foregoing operations.
FIGS. 1 and 2 are views useful in explaining a combinatorial weighing apparatus for practicing the foregoing weighing method, in which FIG. 1 is a schematic view showing the general features of the apparatus, and FIG. 2 is a block diagram of a combination control unit. Numeral 11 in FIG. 1 denotes a main feeder of vibratory conveyance type. Articles to be weighed are introduced into the main feeder 11 and imparted with vibratory motion for a predetermined length of time so as to be dispersed radially outward from the center of the main feeder. Numerals 12, 12 . . . denote n-number of weighing stations which are arranged around the main feeder 11 along radially extending lines to receive the articles dispersed by the main feeder. Each weighing station 12 includes a dispersing feeder 12a, a pool hopper 12b, a pool hopper gate 12c, a weighing hopper 12d, a weight sensor 12e, and a weighing hopper gate 12f. The dispersing feeder 12a comprises an independently vibratable conveyance device for feeding the articles by means of vibration, or an independently operable shutter. In either case, each dispersing feeder 12a is so arranged that the designated amount of articles received from the centrally located main feeder 11 can be introduced into the corresponding pool hopper 12b disposed below it. The pool hopper gate 12c is provided on each pool hopper 12b in such a manner that the articles received in the pool hopper 12b are released into the weighing hopper 12d when the pool hopper gate 12c is opened. Each weighing hopper 12d is provided with a weight sensor 12e of its own. The weight sensor 12e is operable to measure the weight of the articles introduced into the corresponding weighing hopper, and to apply an electrical signal indicative of the measured weight to the combination control unit 20 shown in FIG. 2. The combination control unit then selects the combination of articles (the "optimum" combination) which gives a total weight closest to the target weight value, as will be described below in further detail. Each weighing hopper 12d is provided with its own weighing hopper gate 12f. A drive control unit 30, shown in FIG. 2, upon receiving the signals from each of the weight sensors, produces a signal to open only the weighing hopper gates 12f of those weighing hoppers 12d that give the optimum combination, these gates 12f discharging the articles from the corresponding weighing hoppers 12d into a common chute 13 where they are collected together. The collecting chute 13 has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers 12d via the hopper gates 12f, which are located above the funnel substantially along its outer rim. The articles received by the collecting chute 13 are collected at the centrally located lower end thereof by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like, which is not shown. The collecting chute 13 is provided with a timing hopper 14 at the lower end thereof for temporarily holding the collected articles. The arrival of an externally applied signal from a packaging machine or the like causes the timing hopper 14 to release the retained articles from the system.
Reference will now be had to the block diagram of FIG. 2 for a description of the combination control unit. Numeral 20 denotes the combination control unit which includes an n-bit (n=10) counter 21 for counting timing pulses TP of a predetermined frequency, and for generating all combinations of n-number of the weighing hoppers. These combinations will also be referred to as "combination patterns" where appropriate. Specifically, for n-number of weighing hoppers, n combinations are possible when each combination is composed of one weighing hopper from the total of n weighing hoppers, n(n-1)/2! combinations are possible when each combination is composed of two weighing hoppers selected from said total, and, in general, n(n-1)(n-2) . . . (n-r+1)/r! combinations are possible when each combination is composed of r-number of weighing hoppers selected from said total of n weighing hoppers. Accordingly, when the n-bit binary counter 21 has counted 2.sup.n -1 timing pulses TP, a total of 2.sup.n -1 different bit patterns, from 000 . . . 001 to 111 . . . 111, will have been generated. Therefore, if correlation is established between the first bit and the first weighing hopper, between the second bit and the second weighing hopper, and between third through n-th bits and the third through n-th weighing hoppers, then the generated bit pattern will be an indication of the above-mentioned combination pattern.
A multiplexer 22, in accordance with the output bit pattern of the counter 21, provides an arithmetic unit 24 with read values (indicative of the weight of the article batches) from the weight sensors 12e of predetermined weighing hoppers. For instance, if the value of the count (the bit pattern) in counter 21 is 1000101011 when n=10, then the arithmetic unit 24 will receive the weight value outputs W1, W2, W4, W6, W10 from the weight sensors 12e attached to the first, second, fourth, sixth and tenth weighing hoppers, respectively. A target weight register 23, for storing a target weight value W.sub.a, is connected to the arithmetic unit 24 to apply W.sub.a thereto. The arithmetic unit 24 computes, and delivers the absloute value of the difference between the total weight .SIGMA.W.sub.i, delivered by multiplexer 22, and the target weight value W.sub.a. More specifically, the arithmetic unit 24 performs the operation: EQU .vertline..SIGMA.W.sub.i -W.sub.a .vertline.=A (1)
and produces A, representing the difference (hereafter referred to simply as the "deviation") between the total weight .SIGMA.W.sub.i of the combination and the target weight value W.sub.a. Numeral 25 denotes a minimum deviation register whose initially set value is the target weight value W.sub.a, but whose content is thenceforth updated in a manner to be described later. An optimum combination memory for storing the optimum combination pattern is designated at numeral 26. Numerals 27, 28 denote gates, and 29 a comparator which compares the magnitude deviation A, namely the output of the arithmetic unit 24, with the magnitude of the minimum deviation, denoted by B, stored in the minimum deviation register 25. When the inequality A&lt;B holds, the output of comparator 29 is such that the deviation value A is delivered for storage to the minimum deviation register 25 through the gate 27, and the content (combination pattern) of counter 20a is delivered for storage to the optimum combination memory 26.
The output of the optimum combination memory 26 is applied to a drive control unit 30 which, in accordance with the optimum combination bit pattern received from memory 26, opens the specified weighing hopper gates 12f (FIG. 1), causing the corresponding weighing hoppers 12d to discharge their articles into the chute 13 and, concurrently, causing the corresponding pool hopper gates 12c to open to supply the emptied weighing hoppers 12d with articles afresh.
The operation of the weighing apparatus will now be described. At the beginning, each of the pool hoppers 12b and weighing hoppers 12d contains a supply of the articles. The weight sensors 12e provided on the corresponding weighing hoppers 12d measure the weights of the articles within the respective weighing hoppers and produce the weight values W1 through W10 which are sent to the combination control unit 20. The n-bit (n=10) counter 21 counts the timing pulses TP having the predetermined frequency to produce 2.sup.n -1 combination patterns. Thus, when the first timing pulse TP arrives and is counted, the content of counter 21 becomes 0000000001. As a result, the multiplexer 22 sends the first weight value signal W1, from the weight sensor 12e-1 provided on the first weighing hopper, to the arithmetic unit 24, which responds by performing the operation specified by equation (1) above, thereby producing the signal indicative of the deviation A (=.vertline.W1-W.sub.a) between the total weight of the combination and W.sub.a. Next, the comparator 29 compares A with the content B of the minimum deviation register 25 (the initial value of B being the target weight value W.sub.a). Since the inequality A&lt;B naturally holds, the gates 27, 28 are opened that the deviation value A is transferred to and stored in the minimum deviation register 25, and the content (the combination pattern 0000000001) of n-bit counter 21 is stored in the optimum combination memory 26. Thenceforth, when the second timing pulse TP is generated, the pulse is counted by counter 21, whose content (combination pattern) is incremented to 0000000010. Consequently, the weight value output W2 of the weight sensor 12e provided on the second weighing hopper is delivered to the arithmetic unit 24 which then performs the operation of equation (1) to produce the signal indicative of the deviation value A (=.vertline.W.sub.2 -W.sub.a). The comparator 24 compares the deviation value A with the content B (=.vertline.W.sub.1 -W.sub.a .vertline.) of the minimum deviation register 25. If the relation A.ltoreq.B holds, then neither the register 25 nor the optimum combination memory 26 is updated; if A&lt;B holds, the deviation value A is transferred to and stored in the minimum deviation register 25, and the content of counter 21 is transferred to and stored in optimum combination memory 26. The operation described above is repeated until all 2.sup.n -1 combinations have been generated. At such time, the content of the minimum deviation register 25 will be the minimum deviation value obtained from the 2.sup.n -1 combinations, and the content of the optimum combination memory 26 will be the combination pattern that gave said minimum value. The optimum combination is thus selected from the total of 2.sup.n -1 possible combination patterns.
The optimum combination pattern selected in the above manner is applied to the drive control unit 30 which opens the weighing hopper gates 12f of the weighing hoppers corresponding to the "1" bits in the optimum combination pattern, whereby these weighing hoppers release their articles into the chute 13, this batch of articles making up the optimum combination of articles. This will leave the selected weighing hoppers 12d empty. Subsequently, therefore, the pool hopper gates 12c corresponding to the empty weighing hoppers 12d are opened to introduce a fresh supply of the articles from the respective pool hoppers into said weighing hoppers 12d, leaving these pool hoppers empty. Accordingly, the dispersing feeders 12a which correspond to the empty pool hoppers 12b, are vibrated for a predetermined period of time to deliver a fresh supply of the articles to these pool hoppers. This restores the weighing apparatus to the initial state to permit resumption of the control operation for selecting the best weight combinations in the manner described. Thus, weighing by the combinatorial weighing apparatus may proceed in continuous fashion by repeating the foregoing steps.
With the conventional weighing method as described above, weighing errors can be held below the unit weight of the articles being weighed even when the articles have unit weights differing widely from one to another. Green peppers, for example, vary greatly from one to another in their unit weight. The same is true of potatoes and other agricultural products, livestock foodstuffs such as meats and broilers, and articles in general that cannot be shaped artificially. When weighing candies, snack foods and fabricated metal parts, moreover, the conventional method makes it possible to diminish the average weighing error.
When weighing out a target weight over and over with the prior-art method, however, the weighing error differs with each weighing operation, with the possibility that, ultimately, the total weight of a combination will no longer exist in the neighborhood of the target weight. For example, let us assume that from several dozen to several thousand articles having a comparatively small unit weight of about 5 g or less are to be gathered together and weighed out to a predetermined weight. The weighing error not only frequently exceeds the unit weight in such case, but is known to grow as large as 20 to 30 g. When a combined weight no longer exists near the target weight value, the conventional practice is to charge additional articles into each of the weighing stations to alter the weight in each station, followed by recomputing combinations. With such method, however, too large a value is likely to be weighed out owing to an excessive supply of the articles, thereby leading to a much greater weighing error.